Fluorescent (FL) technique has emerged as a mainstream research and development area in science and engineering, particularly in the field of analytic chemistry and biological science, thanks to its high sensitivity, low-background noise and broad dynamic range, etc. A great number of fluorescent probes have been investigated and widely used in biotechnology.
Since the chemistry of saccharide and related molecular species plays a significant role in the metabolic pathway of living organisms, determining the presence and concentration of biologically important sugars in aqueous media solution, particularly D-glucose (Glu) which is a ubiquitous fuel for biological processes, is necessary in various medicinal and industrial contexts, such as diabetic monitoring. However, distinguishing D-Glu from other structurally similar monosaccharides, such as D-galactose (Gal), D-fructose (Fru) and D-mannose (Man) remains a daunting challenge, although the pioneering works have been done by Shinkai and coworkers (T. D. James, et al. Nature, 1995, 374, 345).
Through elaborate molecular structural designs, FL sensors with preferential binding to Glu have been developed in the past decade (T. D. James, et al. J. Am. Chem. Soc. 1995, 117, 8982; V. V. Karnati, et al. Bioorg. Med. Chem. Lett. 2002, 12, 3373; H. Eggert, et al. J. Org. Chem. 1999, 64, 3846; U.S. Pat. No. 5,503,770; U.S. Pat. No. 5,763,238). In a typical example, two phenylboronic acid (PBA) units were attached to a fluorophoric molecule at the “correct” positions to ensure the formation of 1:1 complex between the PBA probe and Glu analyte. A photoinduced electron transfer process was utilized to incite an FL turn-on response to the Glu binding. The Glu selectivity of such an affinity-dependent FL sensor, however, is rather limited because the PBA unit has a stronger affinity to other saccharides (e.g., Fru, Gal, and Man) than to Glu.
Accordingly, there has been a need in the art to develop new FL sensors with improved Glu selectivity. For this, new approaches based on new concepts need to be devised to exclude these non-Glu saccharides from participating in the FL turn-on processes.
In the mean time, it has been recently discovered that a group of nonemissive fluorogenic molecules, such as TPE, are induced to fluoresce efficiently by aggregate formation, so called an “abnormal” phenomenon of aggregation-induced emission (AIE). Both experimental data and theoretic calculations support the rationale that the unusual AIE effect is caused by the restriction of the intramolecular rotation (RIR) process of the phenyl rotors in the aggregate state. See U.S. Patent Application Publication Nos. 2008/0220407; 2008/0009362; 2010/0009362. See also W. Z. Yuan, Adv. Mater. 2010, 22, 2159.